Hb Thessaloniki, a Novel, Hyperunstable, Alpha Globin Variant Detected in Northern Greece

TL;DR

A new, unstable alpha globin variant called Hb Thessaloniki was discovered in Northern Greece, with minimal effects on blood health.

Contribution

The novel hyperunstable alpha globin variant Hb Thessaloniki is identified and characterized in a Greek population.

Findings

Hb Thessaloniki is caused by the HBA1:c.260T>C mutation, replacing Leu86 with Pro.

The variant is hyperunstable, as confirmed by isopropanol testing and structural prediction algorithms.

The variant has minor clinical effects, with only mild hematological changes observed.

Abstract

Background: Haemoglobinopathies are the most common monogenic disorders both in Greece and worldwide. The most effective strategies against them are carrier detection and prenatal testing following genetic risk assessment consultation for couples on the likelihood of their offspring being affected. Case Presentation: A novel alpha globin chain variant, named Hb Thessaloniki, was detected in Northern Greece. The underlying point variation HBA1:c.260T>C (ref. seq. NM_000558.5) was detected in the HBA1 gene, in heterozygosity, during a routinely performed population screening for haemoglobinopathies. The amino-acid residue Leu86 was replaced by a structure disrupting Pro residue, resulting in a hyperunstable product as shown by the isopropanol test and predicted by the Dynamut2 and Alphafold3 algorithms. The haematological phenotype, due to which genetic analysis was performed, presented with mild microcytosis and hypochromia and was also indicative of the presence of an unstable haemoglobin produced in small quantities (variant encoded by HBA1). Since the proband’s partner presented with a normal haematological phenotype, there is no risk of the couple giving birth to an affected offspring. Expanded analysis of the proband’s relatives identified biallelic variants (αParmaα/ααΤhessaloniki) in the proband’s mother, who presented with no apparent clinical findings, expect for slightly reduced haematological indices. Conclusions: The novel Hb Thessaloniki identified, although theoretically hyperunstable, seems to have minor effects on erythrocyte function, as indicated by haematological findings on the proband and his close relatives. Future identification of co-inheritance with HBA pathogenic point variations or deletions may provide further information regarding genetic counselling. In parallel, the usage of structure–function relation-calculating algorithms may enhance our prediction capability for novel variants.

Figures